UMNSVP Mechanical Systems Notes
Introduction This packet is intended to help new team members at the UMN Solar Vehicle Project get started and up to speed on the mechanical design process. It includes many separate handouts that are briefly described in the following table of contents. Some material is from notes that were prepared for an experimental course in Vehicle Dynamics and Design, some is from student reports, and some is from notes and memos to the mechanical team from our old project adviser, Dr. Starr. The Borealis II, Borealis III, Centaurus I, and Centaurus II Structural Reports are included, as well as some "hardware" notes regarding the NGM wheel, rod ends, tubing properties, aircraft fasteners, bearings and snap rings. This packet was largely created by Dr. Starr, and has not been updated much since 2016. The team is working on writing some new chapters based on experiences with the design and construction of Centaurus 1 and Centaurus 2 (2007-2010 timeframe); these new chapters will be added when time permits. Warning: All chapters are PDFs, some are large! Contents [[:File:UMNSVP_MechBible_1_Estimating_Tire_Loads.pdf | 1: Estimating Tire Loads]] *This handout shows how to estimate loads at the bottom of tires for cornering, braking and bump for a three wheeled vehicle, including estimates for the 1987 GM Sunraycer. These loads are used to trace forces through the suspension members. Note the information that is needed to make the estimates. [[:File:UMNSVP_MechBible_2_Tracing_Loads_from_Tires_to_Chassis.pdf | 2: Tracing Loads from Tires to Chassis]] *This handout describes some "packaging issues" regarding the components of a double A-arm suspension as used on the solar cars and FSAE cars, which are discussed in later handouts with specific dimensions. It also shows how Free Body Diagrams of statics can be used to trace forces from the bottoms of tires through the suspension elements. The diagrams are used to show "what holds the car up“. A comparison of two spring locations on an A—am1m is shown, and utilizes methods from Deformable Body Mechanics, including a table of properties of tubing. You should review statics for ways of recognizing directions of forces, two-force members, and force and torque sums. Also, review deform for stress computations for: **members in tension: can adjust area. **slender columns in compression: can adjust l/r. **members in bending: can adjust moment of inertia. *Also, recognize that most suspension members and brackets can initially be treated as "beams", having shear and moment diagrams. [[:File:UMNSVP_MechBible_3_Roll_Centers_&_Suspension_Geometry.pdf | 3: Roll Centers & Suspension Geometry]] *This handout describes the geometry of the double A-arm suspension, including a discussion of "Roll Centers". There are pages taken from two references that focus upon race cars rather than solar cars, but the description of the geometry is valuable. Later handouts will focus upon solar car issues. [[:File:UMNSVP_MechBible_4_Solarcar_Suspension_Issues.pdf | 4: Solar Car Suspension Issues]] *This handout describes some of the issues to be resolved in designing a double A—arm suspension for a solar car, including aerodynamic concerns, packaging, and "no scrub" geometry. The diagram on page 13 shows the final dimensions for the BI front suspension. Much effort goes into determining these values, but when they are nailed down, component detailing can begin. [[:File:UMNSVP_MechBible_5_No_Scrub_Discussion--part1.pdf | 5: No Scrub Discussion -- Part 1]] *This describes an additional feature to include in suspension geometry to achieve no-scrub motion. It discusses what is to be accomplished, but not how. The how will require further analysis. [[:File:UMNSVP_MechBible_6_Steering_Issues.pdf | 6: Steering Issues]] *This handout describes Ackerman steering geometry and a simple view of how it can be approximated. It also includes a description of bump steer and a start on how it is avoided. Further analysis will be needed to show how to eliminate bump steer. [[:File:UMNSVP_MechBible_6b_Bump_Steer_Analysis.pdf | 6b: Bump Steer Analysis]] *This chapter is a 2007 addition, detailing the further analysis mentioned above. [[:File:UMNSVP_MechBible_7_Chassis_Components_&_Construction.pdf | 7: Chassis Components & Construction: Aurora 4]] *ME 5190 Report, Ryan Goad, March 22, 1999. Note the detailed CG analysis with two battery weights. Only two drawings are needed. [[:File:UMNSVP_MechBible_8_Borealis_Chassis_Design_Notes.pdf | 8: Borealis Chassis Design Notes]] *This handout is a memo to the Borealis I Mechanical Team with a sketch and some notes that show a concept for the chassis. The dimensions are based on a detailed drawing from the Aero Team which is included. Note that a swing arm suspension is shown, while in fact Borealis I ended up using a complex rear-facing double-A-Arm arrangement. (This memo moved the Mech Team off of square one). [[:File:UMNSVP_MechBible_9_Evolution_of_the_BII_Chassis_Dimensions_from_BI.pdf | 9: Evolution of the BII Chassis Dimensions from BI]] *The Borealis I body had an upper and lower potion that were separated by a seamline about halfway up the on body exterior like a clamshell. This caused the top of the body, where the array is, to have very low torsional rigidity. For Borealis II, we wanted the upper body to extend to the bottom plane and wrap around to enhance torsional rigidity, like the Aurora 2-4 cars. At the front, this meant "wrapping" the nose below battery box, if the box was located where it was on BI. So we examined means to move the battery box rearward and move the nose forward and trying not to move the CG rearward. This handout consists of two memos to the team to describe these issues. [[:File:UMNSVP_MechBible_10_Borealis_Front_Uprights.pdf | 10: Borealis Front Uprights: Some Considerations]] *These are notes to the Mechanical Team of Borealis which outlines some details that needed to be examined as the from suspension took shape. We were still considering a lower A—arm that had one "leg" that was parallel to the axle line, like the Aurora cars, so a wide cavity would be required in the upright if the legs were to be two-force members. [[:File:UMNSVP_MechBible_11_New_Suspension_Layout_for_Borealis.pdf | 11: New Suspension Layout for Borealis]] *These are notes to the Borealis Mechanical and Aero teams regarding changing the lower A—arm design from the Aurora style, which had a "leg" parallel to the axle line, to a more conventional "A" shape. There is a weight (length) comparison and some discussion of mounting concepts. [[:File:UMNSVP_MechBible_12_Evolution_of_BII_Rear_Swing_Arm.pdf | 12: Evolution of BII Rear Swing Arm]] *A series of memos to the Mech Team that accompanied the development of the BII swing arm rear suspension. The BI rear suspension was a complex, rearward facing double A—Arm arrangement with a long-stroke shock/spring unit acting over the axle, which required chassis structure back to the axle line. We tried to simplify this for BII. Note the level of detail required: the body-chassis dimensions interact with suspension dimensions. 13: Structural Report Requirements *These memos describe the topics to include in the structural report that the American Solar Challenge requires, and the various loading conditions for crash analysis. Note that these documents are archived here for historical purposes, and future races may have different requirements. *Structural Report Requirements, NASC 2005 *Structural Report Requirements, NASC 2008 *Structural Report Requirements, ASC 2010 14: Selected UMNSVP Structural Reports *[[:File:UMNSVP_MechBible_14a_BII_Structural_Report.pdf | 14a: BII Structural Report]] **Note there are some errors in the analysis of the rear suspension loads and stresses *[[:File:UMNSVP_MechBible_14b_B3_Structural_Report.pdf | 14b: B3 Structural Report]] *[[:File:UMNSVP_MechBible_14c_C1_Structural_Report.pdf | 14c: C1 Structural Report]] *[[:File:UMNSVP_MechBible_14d_C2_Structural_Report.pdf | 14d: C2 Structural Report]] ** C2 Structural Report Addendum A ** C2 Structural Report Addendum B [[:File:UMNSVP_MechBible_15_NGM_Wheel_&_Ecopia_Specs.pdf | 15: NGM Wheel & Ecopia Specs]] *These were provided by NGM company; the wheels were used in Aurora 3, 4 and Borealis vehicles. *Note that this document is from 1996, a newer version (from 2000 or so) can be found here [[:File:UMNSVP_MechBible_16_Rod_End_Data.pdf | 16: Rod End Data]] *Pages from catalog 1093 from the Aurora Bearing Company, one of our sponsors. [[:File:UMNSVP_MechBible_17_Properties_of_Tubing.pdf | 17: Properties of Tubing]] *Weights, areas, moments of inertia and radius of gyration data for steel tubing. The geometric based properties (area, moment of inertia, etc.) apply to any material. [[:File:UMNSVP_MechBible_18_Aircraft_nut_&_bolt_data.pdf | 18: Aircraft nut & bolt data]] *Descriptions and dimensions of many of the fasteners used in our solar cars, from the Coast Fabrication catalog. *Note that Nylocs and Jetnuts are not allowed as locking fasteners in the American Solar Challenge since 2008, Flexnuts are the approved solution. In addition, jam nuts are no longer allowed to lock rod ends as of 2010, flexnuts or safety wire must be used. Read the section in the rules and regulations document about allowed fasteners carefully! [[:File:UMNSVP_MechBible_19_Bearing_Data.pdf | 19: Bearing Data]] *A few pages from the SFK bearing catalog for the BII from hub bearings. It shows the kind of information available for bearings, including load data and dimensions. [[:File:UMNSVP_MechBible_20_Snap_Ring_Data.pdf | 20: Snap Ring Data]] *A few pages showing snap ring dimensions, hole sizes, loads, groove dimensions, etc. The part numbers are “fairly“ universal. Category:UMNSVP